Past Climate Change Caused Largest Extinction of Life on Earth, Killing 70% of Organisms, Says Study

A devastation of conifer forests about 250 million years ago was caused by tree-killing fungi whose growth was triggered by global climate change, says a University of California, Berkeley, study that warns it could happen again.

The study, published online Aug. 5, will appear in the print edition of the journal Geology in September.

In what is considered the largest extinction of life on earth, 95 percent of marine organisms and 70 percent of land organisms died, due to heavily altered climate caused by high amounts of gas and dust thrown into the atmosphere. According to scientists, the climate change occurred as a result of volcanic eruptions in the region now identified as Siberia.

The scientists say filamentous (thread-like) microfossils commonly preserved in Permian rock are relatives of a group of aggressive and deadly fungi, rhizoctonia, which today is known for members that attack and kill plants.

"Modern rhizoctonia include some of the most ubiquitous plant pathogens, causing root, stem and foliar diseases in a wide variety of plants," said co-author Cindy Looy, UC Berkeley assistant professor of integrative biology, in a U of C release. "Based on patterns of present-day forest decline, it is likely that fungal disease has been an essential accessory in woodland destabilization, accelerating widespread tree mortality during the end-Permian crisis."

The crisis, which occurred when today's continents were part of the supercontinent Pangaea, replaced conifer forests with lycopods (4-foot-tall relatives of today's diminutive club mosses) and seed ferns (pteridosperms). The conifers didn't recover for another 4 to 5 million years, says the study.

Looy and her colleagues, Henk Visscher of the Laboratory of Palaeobotany and Palynology at Utrecht University in the Netherlands and Mark Sephton of the Impacts and Astromaterials Research Centre at Imperial College, London, warn that today's changing climate also could foster pathogenic soil microbes that could accelerate the death of trees already stressed by higher temperatures and drought.

"Pathogenic fungi are important elements of all forest ecosystems," said Visscher. "When an entire forest becomes weakened by environmental stress factors, onslaught of damaging fungal diseases can result in large-scale tissue death and tree mortality."

The researchers say destruction of Earth's protective ozone layer due to high amounts of carbon dioxide and methane in the atmosphere might also have been a factor in destroying coniferous forests. Nevertheless, "whatever (the) sequence of events that triggered ecosystem destabilization on land, the aggressiveness of soil-borne pathogenic fungi must have been an integral factor involved in Late Permian forest decline worldwide," the paper says.

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